The present invention relates, in general, to telemetric medical devices. More particularly, the present invention relates to a novel telemetric medical system which is capable of various medical applications including the measurement of a parameter within a patient""s body, particularly an organ. One such application of the present invention is as an implantable telemetric endocardial pressure system, its associated novel components and their novel methods of use.
In general, the use of implantable medical sensors in a patient is known. One example for an implantable sensor is disclosed in U.S. Pat. No. 4,815,469 (Cohen et al.) incorporated herein by reference. The disclosure is directed to an implantable medical sensor which determines the oxygen content of blood. The sensor includes a miniaturized hybrid circuit that includes light-emitting diode means, phototransistor means, and a substrate to which the light-emitting diode means and phototransistor means are bonded in a desired circuit configuration. The hybrid circuit is hermetically sealed within a cylindrical body made from a material that is substantially transparent to light, such as glass. Feedthrough terminals provide means for making an electrical connection with the hybrid circuit. The light-emitting diode means is driven with a stair-stepped current pulse. The purpose of the sensor is to sense the reflective properties of body fluid, such as blood, for spectrophotometric analysis. In one embodiment, the sensor is embedded within a bilumen pacemaker lead and positioned near the distal electrode of the lead so that the sensor resides within the heart when the lead is implanted within a patient, thereby allowing the sensed oxygen content of the blood within the heart to be a physiological parameter that can be used to control the pacing interval of a rate-responsive pacemaker.
U.S. Pat. No. 5,353,800 (Pahndorf et al.) discloses an implantable pressure sensor lead having a hollow needle adapted to be screwed into a patient""s heart. The pressure sensor is supplied electrical power through conductors in the sensor.
There are cases where permanent positioning of the sensor is needed. One such case, for example, is disclosed in U.S. Pat. No. 5,404,877 (Nolan et al.), which is incorporated herein by reference. A leadless implantable cardiac arrhythmia alarm is disclosed which continuously assesses a patient""s heart function to discriminate between normal and abnormal heart functioning and, upon detecting an abnormal condition, generates a patient-warning signal. The alarm is capable of sensing impedance measurements of heart, respiratory and patient motion and, from these measurements, generating an alarm signal when the measurements indicate the occurrence of a cardiac arrhythmia. It is important to note that the sensor uses an antenna system having a coil inductor for generating an electromagnetic field into tissue for detecting changes in impedance which relate to a physiological phenomena. For example, the size of the inductor is preselected in order to match the dimensions of the organ or structure to be measured.
There are also several known implantable devices that employ telemetry for transmitting or receiving data from an external device. One such device is, for example, the system disclosed in U.S. Pat. No. 6,021,352 (Christopherson et al.). The device utilizes a pressure sensor as a transducer for sensing respiratory effort of the patient. Respiratory waveform information is received by an implantable pulse generator (IPG)/simulator from a transducer and inspiration synchronous simulation is provided by the IPG.
One other telemetric implantable device is disclosed in U.S. Pat. No. 5,999,857 (Weijand et al.). This reference discloses a telemetry system for use with implantable devices such as cardiac pacemakers and the like, for two-way telemetry between the implanted device and an external programmer. The system employs oscillators with encoding circuits for synchronous transmission of data symbols in which the symbols form the telemetry carrier. The system provides circuits for higher density data encoding of sinusoidal symbols, including combinations of BPSK, FSK, and ASK encoding. Embodiments of transmitters for both the implanted device and the external programmer, as well as modulator and demodulator circuits, are also disclosed. It is important to note that the implant device has its own power supply in the form of a battery for powering all of the circuitry and components of the implanted device.
It is also important to note, that to date, there has not been any telemetric medical system that is both a highly efficient system due to its components and their ease of use while providing extremely accurate information regarding a measured parameter in a patient""s body.
The present invention is directed to a novel telemetric medical system for use with various medical applications such as monitoring medical conditions or measuring parameters within a patient""s body for different types of organs, including tissue, as well as their function.
The present invention is a telemetric medical system comprising a telemetric medical sensor for implantation in a patient""s body for measuring a parameter therein. The sensor comprises a housing, and a membrane at one end of the housing, wherein the membrane is defonnable in response to the parameter. A microprocessor, which is in the form of a microchip, is positioned within the housing and operatively communicates with the membrane for transmitting a signal indicative of the parameter.
A signal reading and charging device is locatable outside of a patient""s body and communicates with the sensor. The signal reading and charging device comprises a casing and a circuit within the casing. The circuit comprises a logic control unit and a processing unit operatively connected to the logic control unit. The logic control unit, through a deep detector, receives the transmitted signal from the sensor. The logic control unit also sends a powering signal to the sensor through a sine wave driver for remotely powering the sensor. The powering signal is a sinusoidal wave signal approximately 4-6 MHz. The processing unit includes an algorithm for converting the transmitted signal received from the sensor into a measured parameter. Additionally, the signal reading and charging device includes a power source operatively connected to the circuit and a power switch for activating and deactivating the device.
The signal reading and charging device also includes an antenna coil for sending the powering signal to the sensor and for receiving the transmitted digital signal from the sensor. The antenna coil has inductive coupling with the sensor. The signal reading and charging device also includes a display, which is an LCD screen, for displaying the measured parameter.
The microprocessor, which is in the form of a microchip, comprises an array of photoelectric cells which are arranged in staggered rows. The array also includes a reference photoelectric cell located at one end of the array. A light emitting diode (LED) transmits light at the photoelectric cells and the reference photoelectric cell.
The sensor further comprises a shutter connected to the membrane and moveable between the photoelectric cells and the LED in response to the deforming of the membrane. The sensor is arranged such that the reference photoelectric cell is not blocked by the shutter and remains exposed to the light emitted by the LED.
The microchip further comprises a plurality of comparators operatively connected to the photoelectric cells and a buffer operatively connected to the comparators for storing and transmitting the digital signal. The sensor further comprises an antenna, in the form of a coil, operatively connected to the microchip wherein the antenna is located at the exterior of the housing. Alternatively, the antenna is located within the housing of the sensor. Preferably, the antenna coil is made of wire comprising silver and platinum iridium. Additionally, the antenna has 20-25 turns.
The sensor according to the present invention further comprises a plurality of anchoring legs resiliently attached to the housing for anchoring the sensor into tissue. Additionally, the housing optionally includes a notch in an outer surface of the housing to facilitate deployment. The housing further optionally includes a circumferential groove at the notch to furtherer facilitate deployment.
In another embodiment for the sensor, the housing further includes a tapered end and a piercing tip thereon. The tapered end further includes helical threads thereon for threading the sensor housing directly into tissue. An alternative embodiment includes a plurality of tissue barbs on the tapered end for anchoring the sensor housing directly into tissue.
The present invention also includes a method for telemetrically measuring a parameter in a patient""s body comprising the steps of providing a telemetric medical sensor comprising a housing having a membrane at one end of the housing wherein the membrane is deformable in response to the parameter, and a microchip is positioned within the housing and operatively communicates with the membrane for transmitting a signal indicative of the parameter. The sensor is implanted at a site within the patient""s body and the parameter is telemetrically measured from outside of the patient""s body with a signal reading and charging device. The method also includes telemetrically powering the sensor from outside of the patient""s body with the signal reading and charging device. The measured parameter is then displayed on the display of the signal reading and charging device.
The method according to the present invention also includes a method for telemetrically measuring a parameter in a patient""s heart wherein the method comprises the steps of imaging the heart, through the use of transesophageal ultrasonic imaging, and identifying an implantation site in the heart. An opening is created in the tissue at the implantation site and a sensor comprising a housing, a membrane at one end of the housing wherein the membrane is deformable in response to the parameter, and a microchip positioned within the housing and operatively communicating with the membrane for transmitting a signal indicative of the parameter is provided. The sensor is placed within the opening and the parameter is telemetrically measured from outside of the patient""s body based on the transmitted signal by the sensor.
The method also includes telemetrically powering the sensor from outside of the patient""s body and displaying the measured parameter with a signal reading and charging device. Parameter measurements are made multiple times per second with the signal reading and charging device.
According to the present invention, the sensor is positioned within a chamber of the heart by using the septum as an implantation site, for instance, the fossa ovalis. Alternatively, the sensor is positionable at other anatomical sites within the heart and other organs and tissue.
One parameter that is measured with the system and method according to the present invention is hemodynamic blood pressure in a chamber of the heart. Accordingly, the method according to the present invention further includes taking between 10-20 parameter measurements per second.
Moreover, the method further includes creating the opening in the tissue with a needle. In one embodiment of the present invention, the sensor includes a plurality of anchoring legs on the sensor for anchoring the sensor to the tissue. Additionally, the sensor is coated with a nonthrombogenic agent in order to prevent thrombosis within the heart upon implantation of the sensor.
Another embodiment of the method according to the present invention includes a method for telemetrically measuring a parameter in a patient""s heart wherein the method comprises the steps of imaging the heart with transesohageal ultrasonic imaging and identifying an implantation site in the heart. A sensor comprising a housing and a membrane at one end of the housing wherein the membrane is deformable in response to the parameter and a tapered distal end and piercing tip at the other end of the housing is provided. The sensor further comprises a microchip positioned within the housing and operatively communicating with the membrane for transmitting a signal indicative of the parameter. The sensor is implanted at the site with the piercing tip and the tapered distal end of the sensor. The parameter is telemetrically measured from outside of the patient""s body based on the transmission signal by the sensor. Additionally, the sensor is telemetrically powered from outside of the patient""s body. A signal reading and charging device is used outside of the patient""s body to measure the parameter, power the sensor, and display the measured parameter. Accordingly, parameter measurements are made multiple times per second with the signal reading and charging device.
The sensor is positioned within a chamber of the heart and the implantation site is the septum, for instance, at the fossa ovalis. With the system and method according to the present invention, one parameter that is measured is hemodynamic blood pressure within a chamber of the heart. For instance, 10-20 parameter measurements are made per second for monitoring blood pressure in accordance with the present invention.
Alternatively, the sensor includes helical threads on the tapered distal end of the sensor and the sensor is anchored into the tissue at the site by threading the tapered distal end of sensor directly into the tissue. Alternatively, the sensor includes a plurality of tissue barbs on the tapered distal end of the sensor and the sensor is anchored into the tissue at the site with the tissue barbs.